LEDs have increased in popularity due to many advantages, such as: high luminosity, low operational voltage, quick response time, and low power consumption. However, since LEDs are point light sources, how to uniformly distribute the light from LEDs become an issue. This issue is more significant when the LEDs are used as light sources for an application which requires a uniform illumination such as a backlight module for a liquid crystal display (LCD) panel.
Usually, a secondary optical element is used to improve the uniformity of the light from the LEDs. However, it is found that the conventional secondary optical element cannot satisfy the requirement.